Waveguide configurations for optical touch systems

ABSTRACT

The present invention relates to waveguide structures and optical elements for use in an optical touch screen sensor. The waveguide structures and optical elements allow for reduced bezel width and simplified assembly of optical touch screens sensors, and relaxed component tolerances.

FIELD OF THE INVENTION

The present invention relates to input systems, and in particular, optical touch systems having relatively reduced bezel dimensions. However, it will be appreciated that the invention is not limited to this particular field of use.

BACKGROUND OF THE INVENTION

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

Touch screen input devices or sensors for computers and other consumer electronics devices such as mobile phones, personal digital assistants (PDAs) and hand-held games are highly desirable due to their extreme ease of use. In the past, a variety of approaches have been used to provide touch screen input devices. The most common approach uses a flexible resistive overlay, although the overlay is easily damaged, can cause glare problems, and tends to dim the underlying screen, requiring excess power usage to compensate for such dimming. Resistive devices can also be sensitive to humidity, and the cost of the resistive overlay scales quadratically with perimeter. Another approach is the capacitive touch screen, which also requires an overlay. In this case the overlay is generally more durable, but the glare and dimming problems remain.

In yet another common approach, a matrix of infrared light beams is established in front of a display, with a touch detected by the interruption of one or more of the beams. Such “optical” touch screens have long been known (U.S. Pat. No. 3,478,220; U.S. Pat. No. 3,673,327), with the beams generated by arrays of optical sources such as light emitting diodes (LEDs) and detected by corresponding arrays of detectors (such as phototransistors). They have the advantage of being overlay-free and can function in a variety of ambient light conditions (U.S. Pat. No. 4,988,983), but have a significant cost problem in that they require a large number of source and detector components, as well as supporting electronics. Since the spatial resolution of such systems depends on the number of sources and detectors, this component cost increases with display size and resolution.

An alternative optical touch screen technology, based on integrated optical waveguides, is disclosed in U.S. Pat. No. 6,351,260, U.S. Pat. No. 6,181,842 and U.S. Pat. No. 5,914,709, and in US Patent Application Nos. 2002/0088930 and 2004/0201579, each of which is incorporated herein by reference in its entirety. The basic principle of such a device is shown in FIG. 1. In this optical touch screen sensor design, integrated optical waveguides 10 conduct light from a single optical source 11 to integrated in-plane lenses (not shown) that collimate the light in the plane of a screen and/or input area 13 and launch an array of light beams 12 across that screen and/or input area 13. The light is collected by a second set of integrated in-plane lenses (not shown) and integrated optical waveguides 14 at the other side of the screen and/or input area, and conducted to a position-sensitive (i.e. multi-element) detector 15. A touch event (e.g. by a finger or stylus) cuts one or more of the beams of light and is detected as a shadow, with position determined from the particular beam(s) blocked by the touching object. That is, the position of any physical blockage can be identified in each dimension, enabling user feedback to be entered into the device. Preferably, the device also includes external vertical collimating lenses (VCLs) adjacent to the integrated in-plane lenses on both sides of the input area, to collimate the light in the direction perpendicular to the plane of the input area.

The touch screen sensors are usually two dimensional and rectangular, with two arrays (X, Y) of transmit waveguides 16 along adjacent sides of the screen, and two corresponding arrays of receive waveguides 17 along the other two sides of the screen. As part of the transmit side, in one embodiment a single optical source (such as an LED or a vertical cavity surface emitting laser (VCSEL)) launches light via some form of optical power splitter 18 into a plurality of waveguides that form both the X and Y transmit arrays. The X and Y transmit waveguides are usually arranged on an L shaped substrate, and likewise for the X and Y receive waveguides, so that a single source and a single position-sensitive detector can be used to cover both X and Y dimensions. However in alternative embodiments, a separate source and/or detector may be used for each of the X and Y dimensions. For simplicity, FIG. 1 only shows four waveguides per side of input area 13; in actual touch screen devices there will generally be sufficient waveguides for substantial coverage of the input area.

These prior art devices house the waveguide structures that form the X and Y transmit arrays within a protective bezel that surrounds the screen. As will be appreciated, the bezel width necessarily limits the screen size within a given device, which may be a significant limitation for small devices such as mobile phones. A further problem is that, to minimise the bezel width, the distance between the in-plane lenses and the external VCLs should be minimised, leading to a high magnification optical system that is extremely susceptible to errors in the design, fabrication and placement of the external VCLs.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

DISCLOSURE OF THE INVENTION

According to a first aspect the present invention provides a waveguide structure for a touch screen, wherein the touch screen defines a plane, the waveguide structure having at least one optical waveguide adapted to carry a signal for the touch screen, the waveguide structure being configured such that, in use, the at least one optical waveguide extends entirely below the plane.

The touch screen typically includes an upper portion for receiving user input, and in the preferred embodiment, the upper portion defines the plane of the touch screen. The touch screen also includes a periphery defined by a plurality of sides, and is preferably substantially rectangular in shape.

The signal may comprise an input signal or an output signal and is preferably light having a predetermined wavelength. The wavelength may be in the visible region of the spectrum or the infrared region of the spectrum. Desirably the wavelength is between 700 and 1000 nm.

The waveguide structure preferably includes a plurality of optical waveguides, wherein each optical waveguide extends entirely below the plane.

Preferably the waveguide structure is substantially flexible and formed from polymeric materials. Optimally, the waveguide structure is bendable through at least 90° without suffering mechanical damage. In a particularly preferred embodiment, the waveguide structure comprises a plurality of polymer optical waveguides fabricated on a flexible polymer substrate.

Preferably the waveguide structure extends around at least a portion of the periphery. Optionally the waveguide structure extends around adjacent sides of the periphery. However, in preferred embodiments the waveguide structure extends around the entire periphery.

In preferred embodiments, the waveguide structure is disposed substantially perpendicularly to the plane of the touch screen. However, in other embodiments the waveguide structure extends underneath and substantially parallel to the plane of the touch screen, and preferably lies substantially within the periphery.

The waveguide structure is preferably configured such that, in use, the at least one optical waveguide passes through a maximum of two mutually perpendicular planes.

The waveguide structure may be formed as a substantially rectangular two-dimensional sheet. However, in other embodiments, the waveguide structure is formed as a substantially L-shaped two-dimensional sheet.

In a particular embodiment of the invention the Waveguide structure comprises a plurality of input waveguides adapted to carry an input signal and a plurality of output waveguides adapted to carry an output signal. Preferably the input waveguides are grouped on the waveguide structure to define a transmit section, and the output waveguides are grouped on the waveguide structure to define a receive section. Typically, the input waveguides are referred to as transmit waveguides and the output waveguides referred to as receive waveguides. Each waveguide includes an input portion for receiving an input signal and an output portion for transmitting an output signal. Typically the waveguides are positioned such that the input portions of the transmit waveguides and the output portions of the receive waveguides are disposed on a first side of the waveguide structure, and the output portions of the transmit waveguides and the input portions of the receive waveguides are disposed on a second side of the waveguide structure, wherein the first and second sides are substantially mutually opposed. In this embodiment, the input portions of the transmit waveguides are grouped into an input array, and the output portions of the receive waveguides are grouped into an output array, each array extending along a portion of the first side. However, the output portions of the transmit waveguides and the input portions of the receive waveguides are spaced, preferably substantially evenly spaced, along substantially the entire length of the second side.

In other embodiments, the waveguides are positioned such that the input portions of the transmit waveguides and the output portions of the receive waveguides are disposed on opposite sides of the waveguide structure, and the output portions of the transmit waveguides and the input portions of the receive waveguides are disposed on a common side of the waveguide structure. Preferably the output portions of the transmit waveguides and the input portions of the receive waveguides are spaced, preferably substantially evenly spaced, along substantially the entire length of the common side.

The input array is suitably optically coupleable with a light source and the output array is optically coupleable with a light detector, which is preferably a position-sensitive detector.

In preferred embodiments the output portions of the transmit waveguides and the input portions of the receive waveguides include an integral structure, such as a planar lens. In other embodiments the integral structure may be a planar internally reflective mirror.

Preferably the waveguide structure includes at least one fold line defined by a line of weakness to assist in folding the waveguide structure about the periphery of a touch screen. In alternative embodiments, the fold line may be a printed mark to assist in manual assembly with a touch screen and/or with the optical element. Alternatively, a printed mark may be visible to a machine vision system when the waveguide structure is machine assembled with the touch screen.

According to a second aspect the present invention provides an optical element for a touch screen, wherein the touch screen defines a plane, the optical element comprising:

a first reflective surface; and a connect portion adapted for connection to a waveguide structure having at least one optical waveguide adapted to carry an input or an output signal for the touch screen; the optical element being configured for use with the touch screen such that, in use, the first reflective surface is positioned above the plane to re-direct the signal to and from the waveguide, the connect portion being at least partially below the plane whereby the at least one optical waveguide extends entirely below the plane. The reflective surface may be a mirror adapted for optical communication with the connect portion. The mirror may be plane or arcuate in cross-section and is optionally metallised. However, in a preferred embodiment the first reflective surface is an internally reflective surface.

Preferably, the optical element further includes a body of light transmissive material for transmission of the signal between the connect portion and the first reflective surface, in which case the first reflective surface is an internally reflective surface. More preferably, the internally reflective surface is a totally internally reflective surface. Preferably the first reflective surface is curved thereby to focus the signal in a direction substantially perpendicular to the plane of the touch screen. Alternatively, the first reflective surface may be planar so that it does not focus the signal.

In further aspects, the optical element includes a second reflective surface that, in use, is positioned below the plane of the touch screen. An optical element having a second reflective surface is particularly useful when the waveguide structure extends underneath and substantially parallel to the plane of the touch screen. Preferably, the second reflective surface is an internally reflective surface, more preferably a totally internally reflective surface. The second reflective surface may be curved so as to focus the signal in a direction substantially perpendicular to the plane of the touch screen. Preferably, the second reflective surface is curved in a cylindrical fashion so as to focus a plurality of signals associated with a plurality of optical waveguides. Alternatively, the second reflective surface may be planar.

In preferred embodiments, the optical element is formed as a strip of plastic material substantially transparent to the signal light (eg in the infrared region of the spectrum) and opaque to light at other wavelengths (eg ambient visible light). The optical element is preferably injection moulded or extruded. Preferably, the optical element is substantially rigid.

When formed as a strip of plastic material, the first reflective surface of the optical element is preferably arcuate in cross section thereby to focus a plurality of signals associated with a plurality of optical waveguides.

In the preferred embodiments where the optical element further includes a body of light transmissive material between the connect portion and the first reflective surface, the optical element includes an optical surface through which light passes as it transits the touch screen. In some embodiments, this optical surface will be planar. Alternatively, it may be arcuate in cross section to form a lens portion thereby to focus the signal in a direction substantially perpendicular to the plane of the touch screen. Preferably, the optical surface is curved in a cylindrical fashion so as to focus a plurality of signals associated with a plurality of optical waveguides. Irrespective of the precise shape of the optical surface, the optical element is preferably shaped such that, in use, the exterior angle between the touch screen and the optical surface is greater than or equal to 90°. In related aspects, the optical element includes a recess such that the optical element is attachable to the touch screen. Further, the waveguide structure may be fixedly attached to the optical element by, for example, gluing.

According to a third aspect the present invention provides an apparatus for use in an input device, comprising: a touch screen defining a plane, and having a periphery defined by a plurality of sides and an upper portion for receiving user input; a waveguide structure having at least one optical waveguide adapted to carry an input or an output signal for the touch screen; and

one or more optical elements extending along at least a portion of the periphery and in optical communication with respective waveguides, each optical element extending from a position below the plane to a position above the plane such that, in use, each optical element transmits the input or the output signal to or from the upper portion to respective waveguides extending entirely below the plane.

According to a fourth aspect the present invention provides a method of transmitting input and output signals for a touch screen device, the touch screen defining a plane and having an upper portion for receiving user input and a periphery, the method of comprising: providing at least one waveguide structure having at least one optical waveguide adapted to carry an input or an output signal for a touch screen, the at least one optical waveguide extending entirely below the plane; providing one or more optical elements along at least a portion of the periphery; and optically coupling the waveguide structure with a respective optical element such that, in use, each optical element transmits the input or the output signal to or from the upper portion to a respective waveguide extending entirely below the plane. Preferably each optical waveguide extends entirely below the plane.

According to a fifth aspect the present invention provides a method of reducing bezel width in a touch screen device, the touch screen defining a plane and having an upper portion for receiving user input and a periphery, the method comprising: providing at least one waveguide structure having at least one optical waveguide adapted to carry an input or an output signal for the touch screen; providing one or more optical elements along at least a portion of the periphery; and optically coupling the at least one optical waveguide with a respective optical element such that, in use, each optical element transmits the input or the output signal to or from the at least one optical waveguide; wherein the at least one optical waveguide is terminated at a position below the plane, and wherein the optical elements extend from above the touch screen plane to a position below the touch screen plane.

Unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 illustrates a typical prior art waveguide-based optical touch screen sensor;

FIG. 2 is a plan view of one embodiment of a waveguide structure according to the present invention;

FIG. 3 is a plan view of another embodiment of a waveguide structure according to the present invention;

FIG. 4 is a plan view of yet a further embodiment of a waveguide structure according to the present invention, wherein the waveguide includes a recess to accommodate electrical connections to the touch screen that the waveguide structure surrounds;

FIG. 5 is a perspective view of one half of the waveguide structure embodiment shown in FIG. 2, shown folded into an L-configuration and ready to be engaged to a touch screen;

FIG. 6 is a perspective view of the waveguide structure embodiment shown in FIG. 2 engaged to a touch screen;

FIG. 7 is a top view of the waveguide structure embodiment shown in FIG. 3 engaged to a touch screen;

FIG. 8 is a plan view of another embodiment a waveguide structure according to the invention;

FIG. 9 is an underside view of a touch screen showing a pair of the waveguide structure embodiments shown in FIG. 8 engaged thereto;

FIG. 10 is a sectional side view of one embodiment of an optical element according to the present invention shown engaged to a touch screen and having a waveguide structure optically engaged thereto, and directing light from the waveguide across the upper surface of the touch screen;

FIG. 11 is a view similar to FIG. 10 but showing another embodiment of an optical element according to the present invention;

FIG. 12 is a view similar to FIG. 10 but showing a further embodiment of an optical element according to the present invention;

FIG. 13 is a view similar to FIG. 10 but showing yet another embodiment of an optical element according to the present invention (all dimensions in mm);

FIG. 14 is a sectional side view of another embodiment of an optical element according to the present invention shown engaged to a touch screen and having a waveguide structure optically engaged thereto, wherein the waveguide structure is positioned beneath and parallel to the touch screen;

FIG. 15 is a view similar to FIG. 14 but showing another embodiment of an optical element according to the present invention;

FIG. 16 is an exploded perspective view of a touch screen, a waveguide structure according to the invention and an optical element according to the invention;

FIG. 17 is a sectional side view of a prior art waveguide-based optical touch screen sensor showing the relatively wide bezel dimension required to accommodate the waveguide structure and associated optics;

FIG. 18 is a sectional side view of the combined waveguide structure and optical element of the present invention engaged to a touch screen showing the relatively reduced bezel dimensions required; and

FIGS. 19(a) and 19(b) show plan and side views of a typical prior art assembly of a transmit waveguide and an external vertical collimating lens.

PREFERRED EMBODIMENT OF THE INVENTION

Referring initially to FIGS. 2 to 9, a waveguide structure 20 for a touch screen 21 is formed as a substantially two-dimensional sheet comprising a plurality of waveguides 22 adapted to carry input signals or output signals for the touch screen 21. The touch screen 21 is substantially rectangular in shape and includes an upper portion 23 that defines a plane 24 for receiving user input, such as the touch of a finger or a stylus.

In the various embodiments as shown in FIGS. 2 to 4, the substantially rectangular waveguide structure 20 is formed from a resilient polymeric material that is substantially flexible. Preferably the waveguide structure 20 is repeatably bendable through at least 90° without being mechanically damaged. For example, FIG. 5 shows of one half of the waveguide structure 20 shown in FIG. 2 folded into an L-configuration and ready to be engaged to a touch screen 21. FIG. 6 shows the entire waveguide structure 20 of FIG. 2 engaged to a touch screen 21, and FIG. 7 shows waveguide structure 20 of FIG. 3 or FIG. 4 engaged to the entire periphery 25 of a touch screen 21. In the embodiment shown in FIG. 8, the waveguide structure 20 is configured as an “L”, rather than a substantially rectangular sheet as shown in FIGS. 2 to 4. This embodiment is particularly useful when, as shown in FIG. 9, the waveguide structure is engaged to the underside of a touch screen 21.

The waveguide structure 20 preferably comprises a plurality of optical waveguides 22 comprising a photo-curable polymer material fabricated on a flexible polymer substrate, for example by a method disclosed in U.S. Patent Application No. 60/796,722 entitled ‘Methods for fabricating polymer optical waveguides on large area panels’, incorporated herein by reference in its entirety. Briefly, this document describes methods for fabricating polymer optical waveguides comprising a three layer structure, wherein at least one of the optical layers is deposited by a two-stage deposition process whereby the second step is a spinning process. The invention disclosed in U.S. 60/796,722 is of particular relevance to the volume production of polymer optical waveguides on large area substrates.

As shown in FIG. 6, the waveguide structure 20 is configured such that, in use, the waveguide structure 20 extends around at least a portion of the periphery 25 of the touch screen 21. Preferably the waveguide structure 20 extends around the entire periphery 25 and is disposed substantially perpendicularly to the plane 24 of a touch screen 21. Importantly, the waveguide structure 20 is engaged to a touch screen 21 such that each of the waveguides 22 extends entirely below the plane 24 of a touch screen 21.

In other waveguide substrate configurations, the waveguide structure 20 is a two-dimensional sheet that extends underneath and substantially parallel to the plane 24 of touch screen 21. One such configuration comprises four waveguide structures 20, each extending along an edge of the touch screen 21. However, in preferred configurations as shown in FIGS. 8 and 9, the waveguide structure 20 is formed on a pair of L-shaped two-dimensional sheets that extend underneath and substantially parallel to the plane 24 of touch screen 21. It will be appreciated that preferably the waveguide structure 20 lies substantially within the periphery 25 of a touch screen 21. However, the waveguide structure 20 could also exceed the periphery 25 of a touch screen 21. In other embodiments, the waveguide structure 20 may lie underneath as well as extend along at least a portion of the periphery 25 of a touch screen 21, however, not extend above the plane 24 of a touch screen 21. Irrespective of the particular embodiment, it will be understood that the waveguide structure 20 of the present invention is configured such that, in use, the waveguides 22 pass through a maximum of two mutually perpendicular planes.

Referring again to the embodiment as shown in FIG. 2, the waveguide structure 20 comprises a plurality of input waveguides 26 adapted to carry a plurality of input signals, and a plurality of output waveguides 27 adapted to carry a plurality of output signals. The input waveguides 26 are grouped on the waveguide structure 20 to define a transmit section 28, and the output waveguides 27 are grouped to define a receive section 29. The input waveguides are typically referred to as transmit waveguides 26 and the output waveguides referred to as receive waveguides 27. Each of the waveguides 26 and 27 includes an input portion for receiving an input signal and an output portion for transmitting an output signal. The transmit and receive waveguides 26 and 27 are positioned on the waveguide structure 20 such that the input portions 30 of the transmit waveguides 26 and the output portions 31 of the receive waveguides 27 are disposed on a first side 32 of the waveguide structure 20, and the output portions 33 of the transmit waveguides 26 and the input portions 34 of the receive waveguides 27 are disposed on a second side 35 of the waveguide structure 20, the first and second sides 32 and 35 being mutually opposed. Further, the input portions 30 of the transmit waveguides 26 are grouped into an input array 36, and the output portions 31 of the receive waveguides 27 are grouped together into an output array 37, with each array 36 and 37 extending along only a portion of the first side 32 for coupling with a source 38 or detector respectively 39. It should be understood that the input array 36 of transmit waveguides 26 may include a splitter 18 for distribution of optical power to the transmit waveguides 26. However, the output portions 33 of the transmit waveguides 26 and the input portions 34 of the receive waveguides 27 are spaced, preferably substantially evenly spaced, along substantially the entire length of the second side 35. However, it will be appreciated that the spacing may be selected for the particular application.

Referring again to the embodiments as shown in FIGS. 3 and 4, the waveguides 22 are positioned such that the input portions 30 of the transmit waveguides 26 and the output portions 31 of the receive waveguides 27 are disposed on opposite sides of the waveguide structure 20. The output portions 33 of the transmit waveguides 26 and the input portions 34 of the receive waveguides 27 are disposed on a common side of the waveguide structure 20 and spaced along substantially the entire length of the common side 35. Preferably the waveguides are substantially evenly spaced, however it will be appreciated that the spacing may be selected for the particular application.

The input array 36 is optically coupleable with a light source 38 for supplying a light signal and the output array 37 is optically coupleable with a suitable light detector 39. The light has a predetermined wavelength that may, for example, be in the infrared region of the spectrum, preferably between 700 and 1000 nm. Alternatively, the predetermined wavelength may be in the visible region of the spectrum.

Referring in particular to the embodiment as shown in FIG. 8, the output array 37 is disposed at the terminus of one leg of the L-shaped waveguide structure 20, and the input portions 34 of the receive waveguides 27 are substantially evenly spaced along substantially the entire length of the two outer edges of the L-shaped waveguide structure 20, thereby to define an L-shaped receive section. It will be appreciated that an essentially identical arrangement to that shown in FIG. 8 would function as a transmit L-shaped waveguide structure 20.

Additionally, waveguide structures can be overlapped to ensure that the entire periphery 25 of a touch screen 21 is accessible to either the transmit section 28 or receive section 29 of the waveguide structure 20. For example, the waveguide structures shown in FIG. 3 and FIG. 4 can be folded around the periphery 25 of the touch screen 21 with the source 38 and detector 39 overlapped in one corner, as clearly shown in FIG. 7. It should be noted that the waveguide structure shown in FIG. 2 requires source 38 and detector 39 to be located below touch screen 21, whereas the waveguide structures shown in FIGS. 3 and 4 allow source 38 and detector 39 to be located beside touch screen 21. The latter two waveguide structures may be preferable if it is important to minimise the depth of the device as a whole. In yet another configuration, the waveguide structure shown in FIG. 8 can be engaged to the underside of a touch screen and the source 38 and detector 39 overlapped with the receive and transmit waveguide structures respectively. It will be appreciated that this overlapping may require a degree of flexibility in waveguide structure 20, for out of plane bending; this will be trivial if, as preferred, the waveguide structure is composed of polymeric materials.

In related embodiments, as shown in FIG. 16, the output portions 33 of the transmit waveguides 26 and the input portions 34 of the receive waveguides 27 include an integral structure in the form of a planar lens 40 for collimating the light in the plane of the touch screen. Alternatively, the integral structure may be a planar internally reflective mirror, as disclosed in US patent application No 2006/0188196 A1, entitled ‘Waveguide design incorporating reflective optics’ and incorporated herein by reference in its entirety.

In the waveguide structures 20 shown in FIGS. 2 to 4, the transmit waveguides 26 and receive waveguides 27 are provided on a single substantially rectangular strip designed to be folded around the entire periphery of the touch screen. It will be appreciated that the larger the touch screen, the longer the rectangular strip needs to be, however this will be limited by the size of the substrate used for waveguide fabrication. The waveguide fabrication techniques disclosed in U.S. Patent Application No. 60/796,722 will clearly be applicable to this situation. If substrate size is a limitation it is of course possible to fabricate the transmit waveguides and receive waveguides on separate substantially rectangular strips, each of which would be folded around two sides of the periphery, for example as shown in FIG. 5.

Irrespective of whether the transmit waveguides and receive waveguides are fabricated on separate strips or a single strip, a key advantage of fabricating the waveguides on rectangular strips, as shown in FIGS. 2 and 3, compared to the prior art L-shaped waveguide structures as shown in FIG. 1, is that it is significantly easier to singulate rectangular structures than L-shaped structures with a dicing saw. It will be noted that the waveguide structure shown in FIG. 4 has a recess 61, designed to facilitate electrical connections to the touch screen 21. Recess 61 will complicate the singulation process, but since the side 62 incorporating recess 61 has no optical interfaces, it can be shaped with a cruder stamping process while the straight sides are diced. Furthermore, an advantage of the L-shaped configuration shown in FIG. 8 is that the inner edges of the L-shaped waveguide structure of the invention can be shaped with a cruder stamping process since there are no optical interfaces along these edges. The outer edges, having the optical interfaces, can be cut with a dicing saw. In contrast, prior art L-shaped waveguide structures as shown in FIG. 1 have the optical interfaces disposed along the inner edges of the L-shaped waveguide structure, making the dicing process more difficult and costly. It will be appreciated that if the output portions 33 of the transmit waveguides 26 and the input portions 34 of the receive waveguides include an integral structure in the form of a planar lens with a curved optical interface, the singulation process will cut the substrate close to but not at the optical interface. Nevertheless this requires the precision of a dicing saw and is not suited to a stamping process.

As discussed above, the waveguide structure 20 is substantially flexible for assisting in folding around the periphery 25 of a touch screen 21. In other embodiments, the waveguide structure 20 includes at least one fold line 41 defined by a line of weakness to assist in the installation around the touch screen 21. In alternative embodiments, the fold line 41 is a printed mark visible to a machine vision system when the waveguide structure 20 is machine assembled with a touch screen 21 and/or with the optical element 42. Alternatively a printed mark may assist with manual assembly of the waveguide structure 20 with a touch screen 21 and/or with an optical element 42.

Turning now to FIGS. 10 to 15, an optical element 42 for a touch screen 21 is shown comprising a first reflective surface 43 for reflecting a light signal 44 in a direction substantially parallel to the plane 24, and a connect portion 45 adapted for connection to the waveguide structure 20. The optical element 42 is configured for use with a touch screen 21 such that, in use, the first reflective surface 43 is positioned above the plane 24 of a touch screen 21 to re-direct a light signal 44 to or from the waveguide structure 20. Preferably the connect portion 45 is at least partially below the plane 24.

The optical element 42 further includes a body of light transmissive material 46 for transmission of a light signal 44 between the connect portion 45 and the first reflective surface 43.

In other embodiments, as shown in FIGS. 14 and 15, the optical element 42 further includes a second reflective surface 47 that, in use, is positioned below the plane 24, and where the waveguide structure 20 extends underneath and substantially parallel to plane 24 of a touch screen 21.

It will be appreciated that optical element 42 could be constructed such that one or both of the reflective surfaces are externally reflective (ie conventional) mirrors rather than internally reflective surfaces. However a construction where optical element 42 has internally reflective surfaces, as shown for example in FIGS. 10 to 15, is preferred for robustness and ease of manufacture (by injection moulding for example). Further, an externally reflective mirror would need to be metallised, whereas the internally reflective surfaces may not need to be metallised provided the condition for total internal reflection is met. Those skilled in the art will understand that this can be ensured by appropriate design of the optical element.

As shown in FIG. 16, optical element 42 is preferably formed as an elongate strip of plastic material substantially transparent to the signal light (eg infrared light). Desirably, the optical element 42 is opaque to light of other wavelengths (eg ambient visible light if the signal comprises infrared light). The optical element 42 may be injection moulded or extruded and is preferably substantially rigid.

First internally reflective surface 43 may be curved thereby to focus a light signal 44 in a direction substantially perpendicular to the plane 24 of touch screen 21, as shown for example in FIGS. 10-12 and 15. Alternatively, first internally reflective surface 43 may be planar, as shown for example in FIGS. 13 and 14. Second internally reflective surface 47, where present, may likewise be curved or planar. If either the first or the second internally reflective surface is curved, it is preferably curved in a cylindrical fashion so as to focus a plurality of signals associated with a plurality of waveguides.

As shown in FIGS. 10 to 15, the optical element 42 has an optical surface 48 through which light 44 passes as it transits a touch screen 21. In some embodiments, for example as shown in FIGS. 10, 12 and 15, this optical surface 48 may be planar. Alternatively, as shown for example in FIGS. 11, 13 and 14, it may be curved to form a lens portion 49 so as to focus a light signal 44 in a direction substantially perpendicular to the plane of a touch screen 21. Preferably, lens portion 49 is curved in a cylindrical fashion so as to focus a plurality of signals associated with a plurality of waveguides. Irrespective of the precise shape of the optical surface 48, the optical element 42 is preferably shaped such that, in use, the exterior angle between the touch screen 21 and the optical surface 48 is greater than or equal to 90°, to minimise the build-up of dirt over time which could potentially obscure optical surface 48. In other embodiments, the optical elements engaged to the transmit and receive sections of the waveguide structure have different optical surfaces. For example, the transmit optical elements may have a planar optical surface and the receive optical elements may have an optical surface in the form of a lens.

Preferably the optical element 42 includes a recess 50 such that the optical element 42 is attachable to a touch screen 21. In certain embodiments the optical element 42 is configured as a single piece having physical dimensions matching the periphery 25 of a touch screen 21 such that the optical element 42 is adapted to “clip” onto a touch screen 21. Alternatively, the optical element 42 can be glued onto a touch screen 21. In other embodiments the optical element 42 may be configured as two L-shaped pieces each adapted to clip around two adjacent sides of a touch screen 21, or as four straight pieces each adapted to be attached to one side of a touch screen 21 (as shown in FIG. 16).

The waveguide structure 20 may be fixedly attached to the optical element 42 by gluing. However, it will be appreciated that any method of attachment that provides sufficient and stable optical communication between the waveguides 22 and optical element 42 will be suitable.

A particularly preferred design for optical element 42 is shown in FIG. 13, with internally reflective surface 43, recess 50 and optical surface 48 comprising a lens portion 49. In this particular design, internally reflective surface 43 is a plane surface inclined at an angle of 49° to the horizontal, and lens portion 49 forms an exterior angle of approximately 90° with touch screen 21 such that there is no re-entrant cavity between the two where dirt may collect. Because internally reflective surface 43 is angled at 49° to the horizontal, instead of 45°, lens portion 49 is still able to collimate signal light 44 parallel to the surface of touch screen 21.

Referring now to FIG. 16, an apparatus for use in an input device is shown comprising a touch screen 21, a pair of waveguide structures 20, and four optical elements 42. The pair of waveguide structures 20 correspond to a transmit waveguide structure and a receive waveguide structure which, together, extend along the entire periphery 25 of a touch screen 21. The four optical elements 42 are engaged to the waveguide structures 20 in use and are in optical communication with respective waveguides 22. However, it will be appreciated that a pair of L-shaped optical elements, or a one-piece optical element would also be suitable. It will be appreciated that each of the optical elements 42 extend from a position below the plane 24 of a touch screen 21 to a position above the plane 24 such that each optical element 42 transmits input or output signals to or from the upper portion to respective waveguides 22, which extend entirely below the plane 24. The planar lenses 40 of each waveguide 22 can be seen in FIG. 16. These lenses 40 collimate light into and from the optical elements 42, such that signal beams passing across the upper portion 23 of touch screen 21 are focused in the plane 24 of touch screen 21.

In one example, the present invention includes a method of transmitting input and output signals for a touch screen device. The method comprises providing a waveguide structure 20, providing one or more optical elements 42, and then optically coupling the waveguide structure 20 with a respective optical element 42 such that, in use, each optical element 42 transmits input or output signals to or from the upper portion 23 of a touch screen 21 to a respective waveguide 22 extending entirely below the plane 24 of a touch screen 21.

In a further example, the present invention includes a method of reducing the bezel width in a touch screen device. The method comprises providing a waveguide structure 20, providing one or more optical elements 42, and then optically coupling the waveguide structure 20 with a respective optical element 42 such that, in use, each said optical element 42 transmits an input or output signal to or from the waveguide structure 20. The optical elements 42 extend from above the touch screen 21 to a position below a touch screen 21 and the waveguides 22 are terminated at a position below the plane 24.

Referring to FIGS. 17 and 18, it will be appreciated that the present invention provides substantially reduced bezel 51 dimensions compared with prior art devices. The bezel 51 requirements for the present invention (FIG. 18) essentially comprise a thin raised “lip” 52 surrounding a touch screen 21. In contrast, the bezel 51 requirement for prior art devices (FIG. 17) comprises a relatively wide raised flange 53 surrounding a touch screen 21.

In yet a further example, the present invention includes a method of reducing the tolerance required of an optical element used to provide focussing of optical signals in a direction substantially perpendicular to the plane of a touch screen. To illustrate, FIGS. 19(a) and 19(b) show plan and side views of a typical prior art assembly of an output portion 33 of a transmit waveguide 26 having an external vertical collimating lens (VCL) 70, wherein transmit waveguide 26 and VCL 70 are mounted on a common base 71. An essentially identical arrangement is normally present on the receive side. Typically, transmit waveguide 26 comprises a substrate 72, a lower cladding layer 73, a core layer 74 and an upper cladding layer 75, with core layer 74 terminating with an integrated planar lens 40 that collimates light signal 44 in the plane of the touch screen. Note that substrate 72, lower cladding layer 73 and upper cladding layer 75 have been omitted from FIG. 19 a, for clarity. It will be appreciated that a light signal 44 launched from end face 76 of planar lens 40 will diverge in the direction perpendicular to the plane of a touch screen. As a consequence it is often desirable for light signal 44 to be also focussed in this direction. However, such ‘out of plane’ focussing requires a lens having curvature in that direction, which is difficult to shape reliably with photolithographic techniques. Preferably an external lens is employed for this task, for example a VCL 70. VCL 70 is generally curved in a cylindrical fashion so as to focus a plurality of signals associated with a plurality of waveguides.

It will be appreciated that gap 77 between end face 76 of planar lens 40 and curved face 78 of VCL 70 contributes to the overall bezel width in a prior art device, and should ideally be minimised. However this requires VCL 70 to be a relatively powerful lens, ie to have a small radius of curvature. Those skilled in the art of micro-optics will understand that such a high magnification optical system is extremely susceptible to errors in the design, manufacture and placement of VCL 70.

The present invention on the other hand may provide such ‘out of plane’ focussing via optical element 42, several embodiments of which are shown in FIGS. 10 to 15. For example, ‘out of plane’ focusing may be provided by lens portion 49 and/or first reflective surface 43 and/or second reflective surface 47 (if present). Particularly notable are the embodiments shown in FIGS. 13 and 14, where ‘out of plane’ focussing is provided by lens portion 49, such that the distance between the waveguides and the lens portion 49 is greatly increased compared to gap 77 of the prior art device. Consequently the optical elements (lenses or curved reflective surfaces) that provide out of plane focussing do not need to be as powerful as in the prior art, and are therefore more tolerant to manufacture and assembly errors. Further, an optical element 42 may be designed such that two or more of lens portion 49, first reflective surface 43 and second reflective surface 47 (if present) provide the ‘out of plane’ focussing in combination, as shown for example in FIG. 11. Such an arrangement may further relax the tolerances required for the optical element, since an optical system comprising two or more weaker focussing elements in series is generally more tolerant to alignment ‘errors’ than a system of equivalent magnification comprising a single relatively more powerful optical element.

It will be appreciated that the illustrated apparatus of the present invention provides many advantages over prior art devices, including but not limited to the following:

-   -   1.) Mounting the waveguide structure and the optical element of         the present invention to a touch screen allows the bezel         dimensions to be relatively reduced compared to prior art         devices.     -   2.) The waveguide structures of the present invention provide a         number of cost savings compared to prior art L-shaped waveguide         structures. For example, from a manufacturing perspective it is         relatively simpler to singulate a waveguide structure configured         in rectangular stripes than an L-shaped waveguide structure.     -   3.) Assembling an input device utilising the waveguide structure         and optical element of the present invention is relatively         cheaper compared to assembling prior art devices. Additionally,         the present invention requires relatively fewer components than         prior art devices.     -   4.) The configuration of the waveguide structure of the present         invention means that the source and detector can be physically         located adjacent to each other, or preferably, on the same chip.         This simplifies the layout of the internals of the input device         and reduces production costs.     -   5.) From an aesthetics perspective, a thin bezel “lip”         surrounding the touch screen is more appealing than a relatively         wide flange surrounding the touch screen.     -   6.) The optical element with the waveguide structure attached         thereto can be fabricated as a single unit having physical         dimensions matching the periphery of the touch screen. The         optical element can then be simply clipped onto the touch screen         thereby avoiding alignment issues and simplifying installation         and reducing the installation costs.     -   7.) The apparatus and methods of the present invention enable a         relatively larger touch screen to be provided on the device for         the same overall dimensions because the bezel space requirements         are now reduced. This satisfies the intent of many designers,         which is to make the touch display as wide as the device itself,         with almost no excess width. The advantage of this is that the         user obtains the largest possible display size for a given         device size, which is both practical and aesthetically pleasing.     -   8.) The apparatus and methods of the present invention relax the         tolerances on the design, manufacture and placement of optical         elements used to focus the optical signals in the direction         perpendicular to the touch screen.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. 

1. A waveguide structure for a touch screen, wherein said touch screen defines a plane, said waveguide structure having at least one optical waveguide adapted to carry a signal for said touch screen, said waveguide structure being configured such that, in use, said at least one optical waveguide extends entirely below said plane.
 2. A waveguide structure according to claim 1 wherein said touch screen includes an upper portion for receiving user input.
 3. A waveguide structure according to claim 2 wherein said plane is defined by said upper portion.
 4. A waveguide structure according to any one of the preceding claims wherein said touch screen includes a periphery defined by a plurality of sides.
 5. A waveguide structure according to claim 4 wherein said touch screen is substantially rectangular in shape.
 6. A waveguide structure according to any one of the preceding claims wherein said signal comprises an input signal or an output signal.
 7. A waveguide structure according to any one of the preceding claims wherein said signal is light having a predetermined wavelength.
 8. A waveguide structure according to claim 7 wherein said predetermined wavelength is in the infrared region of the spectrum.
 9. A waveguide structure according to claim 7 wherein said predetermined wavelength is in the visible region of the spectrum.
 10. A waveguide structure according to any one of the preceding claims wherein each said at least one optical waveguide extends entirely below said plane.
 11. A waveguide structure according to any one of the preceding claims wherein said waveguide structure is configured such that, in use, said at least one optical waveguide passes through a maximum of two mutually perpendicular planes.
 12. A waveguide structure according to any one of the preceding claims wherein said waveguide structure is formed from polymeric materials.
 13. A waveguide structure according to any one of the preceding claims wherein said waveguide structure is formed as a substantially rectangular two-dimensional sheet.
 14. A waveguide structure according to any one of the preceding claims wherein said waveguide structure is substantially flexible.
 15. A waveguide structure according to claim 14 wherein said waveguide structure is bendable through at least 90°.
 16. A waveguide structure according to any one of claims 4-15 wherein said waveguide structure extends around at least a portion of said periphery.
 17. A waveguide structure according to any one of claims 4-16 wherein said waveguide structure extends around adjacent sides of said periphery.
 18. A waveguide structure according to any one of claims 4-17 wherein said waveguide structure extends around the entire said periphery.
 19. A waveguide structure according to any one of the preceding claims wherein said waveguide structure is disposed substantially perpendicularly to said plane of said touch screen.
 20. A waveguide structure according to any one of the preceding claims wherein said waveguide structure comprises a plurality of transmit waveguides adapted to carry an input signal to said touch screen and/or a plurality of receive waveguides adapted to carry an output signal from said touch screen.
 21. A waveguide structure according to claim 20 wherein said transmit waveguides are grouped on said waveguide structure to define a transmit section, and/or said receive waveguides are grouped on said waveguide structure to define a receive section.
 22. A waveguide structure according to claim 20 or claim 21 wherein each said waveguide includes an input portion for receiving an input signal and an output portion for transmitting an output signal.
 23. A waveguide structure according to claim 22 wherein said waveguides are positioned such that said input portions of said transmit waveguides and said output portions of said receive waveguides are disposed on a first side of said waveguide structure, and said output portions of said transmit waveguides and said input portions of said receive waveguides are disposed on a second side of said waveguide structure.
 24. A waveguide structure according to claim 23 wherein said first and second sides are substantially mutually opposed.
 25. A waveguide structure according to claim 23 or claim 24 wherein said input portions of said transmit waveguides are grouped into an input array, and said output portions of said receive waveguides are grouped into an output array, each said array extending along a portion of said first side.
 26. A waveguide structure according to any one of claims 23-25 wherein said output portions of said transmit waveguides and said input portions of said receive waveguides are substantially evenly spaced along substantially the entire length of said second side.
 27. A waveguide structure according claim 22 wherein said waveguides are positioned such that said input portions of said transmit waveguides and said output portions of said receive waveguides are disposed on opposite sides of said waveguide structure, and said output portions of said transmit waveguides and said input portions of said receive waveguides are disposed on a common side of said waveguide structure.
 28. A waveguide structure according claim 27 wherein said output portions of said transmit waveguides and said input portions of said receive waveguides are substantially evenly spaced along substantially the entire length of said common side.
 29. A waveguide structure according to any one of the preceding claims wherein said waveguide structure includes at least one fold line defined by a line of weakness or printed indicia.
 30. A waveguide structure according to any one of claim 4-12 wherein said waveguide structure is formed from one or more substantially L-shaped two-dimensional sheets.
 31. A waveguide structure according to claim 30 wherein said waveguide structure extends underneath and substantially parallel to said plane of said touch screen.
 32. A waveguide structure according to claim 30 or claim 31 wherein said waveguide structure lies substantially within said periphery.
 33. A waveguide structure according to any one of claims 30-32 wherein said waveguide structure comprises a plurality of transmit waveguides adapted to carry an input signal to said touch screen, or a plurality of receive waveguides adapted to carry an output signal from said touch screen.
 34. A waveguide structure according to claim 33 wherein each said waveguide includes an input portion for receiving an input signal and an output portion for transmitting an output signal.
 35. A waveguide structure according to claim 34 wherein said waveguides are positioned such that said input portions of said transmit waveguides or said output portions of said receive waveguides are disposed on a first side of said waveguide structure.
 36. A waveguide structure according to claim 35 wherein said first side is the terminus of a leg of said L-shaped two-dimensional sheet.
 37. A waveguide structure according to any one of claims 34-36 wherein said output portions of said transmit waveguides or said input portions of said receive waveguides are substantially evenly spaced along substantially the entire outer edges of said L-shaped two-dimensional sheet.
 38. A waveguide structure according to any one of claims 22-28 and 34-37 wherein said input portions of said transmit waveguides are grouped into an input array, and said output portions of said receive waveguides are grouped into an output array.
 39. A waveguide structure according to claim 38 wherein said input array is optically coupleable with a light source.
 40. A waveguide structure according to claim 38 or claim 39 wherein said output array is optically coupleable with a light detector.
 41. A waveguide structure according to any one of claims 22-28 and 34-40 wherein said output portions of said transmit waveguides and said input portions of said receive waveguides include an integral structure.
 42. A waveguide structure according to claim 41 wherein said integral structure is a planar lens.
 43. A waveguide structure according to claim 41 wherein said integral structure is a planar internally reflective mirror.
 44. An optical element for a touch screen, wherein said touch screen defines a plane, said optical element comprising: a first reflective surface; and a connect portion adapted for connection to a waveguide structure having at least one optical waveguide adapted to carry an input or an output signal for said touch screen, said optical element being configured for use with said touch screen such that, in use, said first reflective surface is positioned above said plane to re-direct said signal to or from said optical waveguide, said connect portion being at least partially below said plane whereby said at least one optical waveguide extends entirely below said plane.
 45. An optical element according to claim 44 further including a body of light transmissive material for transmission of said signal between said connect portion and said first reflective surface.
 46. An optical element according to claim 44 or claim 45 wherein said first reflective surface focuses said signal in a direction substantially perpendicular to said plane.
 47. An optical element according to any one of claims 44 to 46 further including a second reflective surface, such that, in use, said second reflective is surface positioned below said plane.
 48. An optical element according to claim 47 wherein said first and/or said second surface is an internally reflective surface.
 49. An optical element according to any one of claims 44 to 48 wherein said optical element is formed as a strip of plastic material substantially transparent to light of the infrared or visible region of the spectrum.
 50. An optical element according to any one of claims 44 to 49 wherein said optical element is substantially transparent to light of the infrared region of the spectrum and opaque to ambient visible light.
 51. An optical element according to any one of claims 44 to 50 wherein said optical element is injection moulded or extruded.
 52. An optical element according to any one of claims 44 to 51 wherein said optical element is substantially rigid.
 53. An optical element according to any one of claims 44 to 52 further including an optical surface.
 54. An optical element according to claim 53 wherein said optical surface is a lens portion.
 55. An optical element according to claim 54 wherein said lens portion is planar or arcuate in cross-section.
 56. An optical element according to any one of claims 44 to 55 further including a recess such that said optical element is attachable to said touch screen.
 57. An optical element according to any one of claims 44 to 56 wherein said waveguide structure is fixedly attached to said optical element.
 58. An apparatus for use in an input device, comprising: a touch screen defining a plane, and having a periphery defined by a plurality of sides and an upper portion for receiving user input; a waveguide structure having at least one optical waveguide adapted to carry an input or an output signal for said touch screen; and one or more optical elements extending along at least a portion of said periphery and in optical communication with respective waveguides, each optical element extending from a position below said plane to a position above said plane such that, in use, each said optical element transmits said input or said output signal to or from said upper portion to respective waveguides extending entirely below said plane.
 59. A method of transmitting input and output signals for a touch screen device, said touch screen defining a plane and having an upper portion for receiving user input and a periphery, said method of comprising: providing at least one waveguide structure having at least one optical waveguide adapted to carry an input or an output signal for a touch screen, said at least one optical waveguide extending entirely below said plane; providing one or more optical elements along at least a portion of said periphery; and optically coupling said waveguide structure with a respective optical element such that, in use, each said optical element transmits said input or said output signal to or from said upper portion to a respective waveguide extending entirely below said plane.
 60. A method according to claim 59 wherein each said optical waveguide extends entirely below said plane.
 61. A method of reducing bezel width in a touch screen device, said touch screen defining a plane and having an upper portion for receiving user input and a periphery, said method comprising: providing at least one waveguide structure having at least one optical waveguide adapted to carry an input or an output signal for said touch screen; providing one or more optical elements along at least a portion of said periphery; and optically coupling said at least one optical waveguide with a respective optical element such that, in use, each said optical element transmits said input or said output signal to or from said at least one optical waveguide; wherein said at least one optical waveguide is terminated at a position below said plane, and wherein said optical elements extend from above said touch screen to a position below said touch screen.
 62. A waveguide structure for a touch screen, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
 63. An optical element for a touch screen, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
 64. An apparatus for use in an input device, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
 65. A method of transmitting input and output signals for a touch screen device, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
 66. A method of reducing bezel width in a touch screen device, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples. 